To promote bone growth that will strengthen and straighten a spine that is curved as a result of, for example, scoliosis, surgeons may implant a shaped rod next to the spine. The rod must be shaped appropriately for each patient, based on the severity and direction of the curvature of the spine. For accuracy, the surgeon shapes the rod after exposing the spine.
As the surgeon views the exposed spine, he or she may bend the implant rod to the desired shape free-hand, using a conventional rod bender. Alternatively, the surgeon may first bend a pliable template rod by hand to the desired shape, and thereafter use a conventional rod bender to bend the implant rod to correspond to the shape of the template rod. An example of the conventional rod bender is the three-point rod bender discussed in U.S. Pat. No. 4,474,046.
The invention relates to the rod-bending method that includes the use of the template rod. Conventional template rods are marked with a line that signifies the orientation of the rod. Typically, the line faces up as the surgeon begins bending the template rod to fit the patient. Using conventional tools, the implantable rod, which is made of stainless steel or titanium and not easily bent, is placed in a rod holder. The surgeon makes bends in the implant rod that correspond to the bends in the template rod, using the line in the template rod as a visual guide to the required direction and degree of bending.
Generally, the surgeon works with a trained assistant who holds the implant rod at desired orientations while the surgeon positions the rod bender along the rod to make the appropriate bends. The assistant must position the implant rod at the appropriate orientation and then hold the rod securely, avoiding moving the rod laterally and/or rotating the rod while the rod is being bent. As the surgeon bends the implant rod, he or she visually compares the rod with the template rod, to determine if the two rods correspond in shape. The visual comparison must be made in three dimensions, to ensure that the implant rod conforms to all of the bends and displacements of the template rod.
The conventional rod-bending procedure is time consuming, and there is much room for error. For example, an assistant may incorrectly position the implant rod or allow the implant rod to move laterally or rotate while it is being bent, and the implant rod is thus bent incorrectly. The rod must then be re-bent, to correct its shape. Re-bending the rod may cause unnecessary scarring of the implant rod or it may weaken the rod, which leaves the rod prone to stress fractures. If the rod cannot be re-bent to the appropriate shape, a new rod must be started. The re-bending of the old rod or the starting a new rod takes time, and thus, prolongs the surgical procedure. Alternatively, the surgeon may incorrectly determine, through the visual comparison, that the two rods correspond. The result may then be an implant rod that does not conform to the template rod over its entire length, that is, a rod that may not be optimally shaped for the patient.